My friend's T41 (type:2379) has a very unusual symptom. When you unplug the AC adapter, it turns on (even if system is closed. Of course this occurs with the battery in, even tried swapping batteries with both of mine and different adapters. Shutting down on battery will not turn off the system, it just starts back up. It looks like it shuts down, then turns back on.
Also, it will not turn on from the battery alone. If the system is devoid of adapter, and battery, and the battery is reinserted, it will not turn on. I have tried the 'old trick' with the disconnection of all power and depressing the power button, but no changes.
BIOS is up to date, no previous problems, and I have it fully disassembled, no liquid, or physical damage present.
So to recap;
1.) Disconnection of AC adapter turns system on.
2.) Will not shut off on battery (shutdown or hibernate).
3.) If off, will not tun on on battery.
UPDATE: System will not wake-up by disconnecting the AC adapter while in sleep mode.
2nd Update, this is almost like micl9's problem
: differences in red.
When on battery power:
If I shut down via XP - it restarts after shutdown.
If I force a power-down (hold pwr key) - it stays off but will not power back up (pwr key does nothing) until either;
a) I pull the battery and when I reinsert the battery it WILL NOT starts by itself or with power key.
b) I plug into AC pwr - it does not start up by itself, OR when the pwr key is pushed.
[Battery and AC must be disconnected for about a min for the system to be usable again, will only turn on with AC]
When on AC power:
If I shut down via XP - it stays shutdown. And power key functions normally to turn back on.
If I force a power-down (hold pwr key) - it stays off. Battery indicator blinking green. And power key functions normally to turn back on.
If unit is off and I pull the ac power it starts up by itself.
Essentially when on AC power it behaves normally.